tachometer wiring question

[randylindberg]

Happy New Year! #1 resolution: Get every guage, light, buzzer working...whoa!

My tach doesn't work, and before I tear into the guages (yuck) I need to know what wire goes where in the engine compartment? I can't seem to find any info in my manuals that shows what wire controls the tach, and where it might hook to. I found a black wire that has a female end that is floating around near the distributor, but I don't know where it goes (I'm probably opening a can of worms there too!) either. Any help guys? (and gals)

 

[80convertible]

Assuming that your 75 has an electronic tach look at the distributor, you should see two connections under the cap( the cap should also have imprinted at these connections tach, batt). One is for ignition and one is for the tach. If your car is running then the ignition should be connected already, so you would connect your tach to the other. Look for a possible loose wire with a connector that will engage the connection on the distributor. It uses a unique connector. My connector was missing, and someone had wired in a female spade connector. I went to the junk yard and pulled the correct connector off an old Camaro. According to the wiring diagram in my Haynes repair manual one wire is brown and one pink (the book does not show which is tach and ignition). The back of the tach has three wires black, pink and brown. Since it looks like pink supplies multiple gauges, it must be fused power, black for ground and brown from the distributor. I'm not 100% sure on this, just making some assumptions. Regardless, look for a loose wire near the distributor with the proper connector to engage the distributor connection under the cap. My tach was not working, so I cleaned all the connections and the copper on the circuit board and the tach now works perfectly. Check all wires and connections before anything else. The circuit board does not fail that easily.

Jim

 

[randylindberg]

Jim, Thanks for all the info.
I figured out which one is the ignition (car stalled!), and I'm assuming the other is the tach. After removing the clip from the coil I can't really tell how the wire actually is attached to the clip (this is probably so simple I'll regret even stating it...) I don't want to yank it and just start trying new wires, but that might just be what I have to do. It just looks like the wire was pushed in there, but it doesn't want to come out with gentle pressure...
Any suggestions?

 

[80convertible]

Randy,

Is the wire for the tach connected at the distributor? If you stare at the connector for a long time like me, you will see how it connects. Usually you have to use a small flat head screw driver to life up on a part of the connector that is designed to snap around another piece of plastic. Sort of like a safety latch. Kind of hard to explain in words. Just look at it and slowly pry with a small screw driver. You will figure it out. In the event you break the connector you can replace it. Also, do you have a wiring diagram? If it's the one in the Haynes or Chiltons manuals...there are not that great. You need to get either a 75 shop manual or the big lamenated poster that sells for around $20.00 from one of the vette mail order catalogs. I have one and it's a life saver because you can read the wiring schematic in great detail and it's actually large enough print to read and follow along. Helps in these types of situations. Enough with my rambling

Jim

P.S I just went and looked at my distributor. Assuming that your connection is like mine (and I think it should be), use the small flat head screw driver to pry back the very top of the connector (just under the distributor cap). I'm talking about the top part where you see the slit in the middle of the connector. It will disengage from the plastic tab molded into the distributor cap itself and slid back. I hope my wording is not making this more difficult.

 

[randylindberg]

Your wording is just about perfect. I got the connector off just like you said, and I see that both wires are already hooked up, and the coil says TACH and BATT. I know you said you cleaned your connection, how did you get inside the female end of the connector to do this? I tried to scrape it with the same small flat screwdriver, but no luck. Does the wire itself have a male or femal type connector end that inserts into the coil? I just don't really understand how I can get the wire out of the plastic clip to clean it without just pulling on it...'fraid once I pull it out I'll never get it back in! I appreciate your help on what's probably such a novice question!

 

[80convertible]

Randy,

As long as the tach wire is connected at the distributor don't mess with it. If you want to clean it buy some electrical cleaner in a spray can at the store and spray the connector on both the wire and cap. Just make sure those connections are secure. The next thing to check before you pull the instrument cluster is the tach filter. I don't know much about the tach filter as mine is missing on my car. If it fails, the tach won't work. I think it is wired in-line with the tach wire running from the distributor cap to the tach circuit board. Try to follow the wire in the engine comparment and you may see it. I would also do a search on this forum for tach filter. Another forum to search is corvetteforum.com. It has more users, and I know I read a thread about the tach filter. Lastly it could be at the tach itself. You will have to pull the instrument cluster. I can't help you there as my 1980 cluster is different I think. Still its not very hard to pull the cluster. Just go slow and look at how things are connected and fastened. The tach has it's own printed circuit board. I would perform a continuity check on the tach wire from the distributor to the tach circuit board to make sure that wire does not have a break. Do yoy have an electrical current tester? If not get one from Radioshack as you will need it for many projects on the vette. From there clean the printed circuit board with electrical cleaner and a pencil eraser on exposed copper (the pencil eraser will clean oxidation off exposed copper better than anything I know of). If that does not work you just might have to buy a new tach circuit board which is about $60.00. I was able to fix my tach without the need for a new board. You just don't really know until you start to troubleshoot. This is great practice for many projects to come.

Jim